In the context of the measurement of the visual acuity of a patient, it has already been proposed to simulate the visual compensation to be provided, for example by means of trial frames or a refractor such as a phoropter.
Trial frames are able to receive, in succession, trial lenses providing different corrections, until the suitable correction for the patient is found.
This solution is impractical and requires trial lenses to be stored separately in dedicated boxes. It furthermore involves lens changes, resulting in undesired and non-continuous transitions in corrective power.
In phoropters, trial lenses are placed on a plurality of disks that are rotated manually or using a motorized mechanism.
However, it will be understood that such an object has a substantial bulk and weight related to the number of lenses placed on each disk.
In addition, the field of view through the phoropter is limited (tunnel effect) because of the plurality of lenses that are aligned in order to obtain various correctional values.
Before presenting the invention, a few definitions of notions used in the following description will be recalled.
Optical power is the degree to which an optical element is able to make light rays converge or diverge. It is expressed in diopters and corresponds to the inverse of focal length in meters.
Spherical power is spoken of when the optical power is the same in all the meridian planes of the lens (rotational symmetry about the optical axis).
In contrast, astigmatism is spoken of when the optical power varies depending on the meridian of the lens. In the case of an astigmatic optical element, cylindrical power is spoken of i.e. the difference between the maximum optical power along a first meridian and the minimum optical power along a second meridian. This is the case of toric or cylindrical surfaces.